Anesthesia rebreathing apparatus including improved reservoir means

ABSTRACT

Apparatus useful in a general anesthesia rebreathing system comprised of a disposable portion easily coupled to and decoupled from a permanent portion. The disposable portion includes breathing tubing for coupling a source of fresh gas, as from an anesthesia machine, to a patient and in addition, an overflow tube for coupling the patient end of the system to an overflow (pop-off) valve, preferably mounted on the machine and constituting part of the permanent portion. The overflow tube entrance is located close to the patient end of the system and in communication with the tubing which conveys expired gas to a reservoir. The arrangement assures that the patient&#39;&#39;s initially expired dead space gas is conveyed by the tubing to the reservoir with subsequently expired alveolar gas being exhausted through the overflow tube and pop-off valve. The reservoir comprises one chamber of an assembly including two hermetically isolated chambers. The second chamber communicates through a selector valve means with either (1) a flexible container which can be squeezed by an attending anesthetist or (2) a mechanical ventilator. The pop-off valve is operable in two different modes, i.e. (1) as a manually controlled variable orifice for spontaneous ventilation and (2) as an automatically controlled valve responding to a positive control pressure for manually assisted or mechanically controlled ventilation. The control pressure is obtained from the second chamber of the reservoir assembly.

United States Patent 1191 Henkin 1 ANESTHESIA REBREATHING APPARATUS INCLUDING IMPROVED RESERVOIR MEANS [76] Inventor: Melvyn L. Henkin, 19640 Greenbriar Dr., Tarzana, Calif. 91356 221 Filed: May 1, 1974 21 Appl. No.1 465,817

Related US. Application Data [63] Continuation-impart of Set. No. 218,337, Jan. 17,

1972, Pat. No. 3,814,091.

[52] U.S. Cl. 128/188; 128/202; 128/145] [51] Int. Cl A6lm 16/00 [58] Field 01' Search 123/188, 202, 203, 191,

Primary Examiner-Richard A. Gaudet Assistant Exumitmr-Henry J. Recla Attorney, Agent, or Firm-Lindenberg, Freilich, Wasscrman, Rosen & Fernandez [57] ABSTRACT Apparatus useful in a general anesthesia rebreathing DISPOSABLE. A 530, 54a 52a 1451 Aug. 26, 1975 system comprised of a disposable portion easily coupled to and decoupled from a permanent portion. The disposable portion includes breathing tubing for coupling a source of fresh gas, as from an anesthesia machine, to a patient and in addition, an overflow tube for coupling the patient end of the system to an overflow (pop-off) valve, preferably mounted on the machine and constituting part of the permanent portion. The overflow tube entrance is located close to the patient end of the system and in communication with the tubing which conveys expired gas to a reservoir. The arrangement assures that the patients initially expired dead space gas is conveyed by the tubing to the reservoir with subsequently expired alveolar gas being exhausted through the overflow tube and pop-off valve, The reservoir comprises one chamber of an assembly including two hermetically isolated chambers. The second chamber communicates through a selector valve means with either (1) a flexible container which can be squeezed by an attending anesthetist or (2) a mechanical ventilator. The pop-off valve is operable in two difierent modes, 1e. (1) as a manually controlled variable orifice for spontaneous ventilation and (2) as an automatically controlled valve responding to a positive control pressure for manually assisted or mechanically controlled ventilation. The control pressure is obtained from the second chamber of the reservoir as sembly.

10 Claims, 18 Drawing Figures 54 r/ PEQMANeNT FQEsH a 1N WOQKING GAS PATENI'ED E 3,901,230

SHKET 1 0F 5 To VEHTILATOQ l To Exhaust PATENTED 3.901.230

sum 5 [1F 55 ANESTHESIA REBREATHING APPARATUS INCLUDING IMPROVED RESERVOIR MEANS RELATED APPLICATIONS This application is a continuatiomin-part of US. patent application Ser. No. 218,337, filed Jan. I7, 1972, now patent No. 3,814,091 by Melvyn L. Henkin.

BACKGROUND OF THE INVENTION This invention relates generally to apparatus for administering general anesthetics in the gaseous state and more particularly to an anesthesia rebreathing system, comprised of a permanent portion and a disposable portion.

The use of conventional general anesthesia administration apparatus inherently involves the danger of cross contamination between patients, sometimes with fatal results. Typically, such apparatus, for example an anesthesia circle, is comprised of one way valve controlled inspiratory and expiratory tubes communicating between an anesthesia machine providing fresh gases, and a patient. The inspiratory and expiratory tubes generally communicate with the patients lungs via a tubular Y-piece and a mask or endotrachael tube. At the anesthesia machine end of the system, the expiratory tube normally communicates with the upper end of a canister of CO absorber material. The lower end of the canister is coupled to the machine end of the inspiratory tube and to a gas reservoir such as a breathing bag. The fresh gas input from the anesthesia machine is usually coupled to the inspiratory tube close to the breathing bag. On expiration, the patients gas is channeled through the one way valve in the expiratory tube to the CO absorber material. On inspiration, the patients gases are pulled through the inspiratory tube via the one way inspiratory valve, from the breathing bag and fresh gas supply. A pop-off valve is normally located proximate to the CO absorber canister for exhausting expired gas.

It will of course be readily appreciated that in the utilization of such anesthesia apparatus, various parts of the apparatus are exposed to gas expired by the patient who, if infected, will transmit bacteria throughout these parts. It has been found that cultures taken from such patient exposed parts will grow bacteria after the apparatus has been subjected to such cleaning procedures as are considered practical for each particular part of the apparatus.

In recognition of the foregoing contamination problem, recent attempts have been made to sufficiently reduce the cost of anesthesia apparatus so that most of the patient exposed parts can be discarded after a single use. Generally, these attempts have merely involved fabricating conventional apparatus in an inexpensive manner so that disposal is economically feasible. Such attempts have not. however, been too successful because cost reduction has not been sufficiently significant and because such cost reduction has necessitated the introduction of performance compromises which have often adversely affected the reliability and ease of use of various parts, such as the pop off valve.

The parent (Ser. No. 218,337) of this continuationin-part application discloses an anesthesia rebreathing system comprised of a disposable circuit apparatus and a permanent portion configured so as to minimize the structural complexity and cost of the disposable portion. while assuring that the disposable portion includes all elements which are likely to contaminate gas inhaled by a patient. In the first embodiment disclosed in the parent application, the circuit constiw: t. what is generally referred to as a circle, including both inspiratory and expiratory tubes. In the second embodiment disclosed in the parent application, the circuit utilizes a single tube alternately used for inspiration and expiration. Both circuit embodiments incorporate an overflow tube whose entrance communicates with the tubing carrying expired gas, close to the patient. The over' flow tube exits at an overflow (pop-off) valve which is located close to the anesthesia machine where it can be conveniently controlled by the attending anesthetist. By locating the overflow tube entrance close to the patient, the overflow tube functions to preferentially vent alveolar gases, rich in CO through the pop-off valve and save dead space and unbreathed gas, rich in O within the tubing and reservoir for rebreathing. As a consequence, the maximum amount of CO is vented, thus substantialy eliminating the need to use CO absorber material.

Both circuit embodiments in the parent application incorporate a reservoir having flexible walls and arranged such that dead space gas initially expired by a patient is conveyed through the breathing tube to the reservoir with subsequently expired alveolar gas being conveyed through the overflow tube to the pop-off valve. The pop-off valve is disclosed as being operable in two different modes, i.e. (l) as a manually controlled variable orifice for spontaneous ventilation and (2) as an automatically controlled valve responding to a positive control pressure for manually assisted or mechanically controlled ventilation. The source of control pressure is selectable by the attending anesthetist such that the pop'off valve is sealed closed in response to (1) pressure within the circuit for manually assisted ventilation and to (2) pressure produced by a mechanical ventilator for mechanically controlled ventilation.

SUMMARY OF THE INVENTION In accordance with the present invention, a reservoir assembly is provided comprised of two hermetically isolated chambers with the first chamber being defined by flexible walls subjected to the pressure within the second chamber. The second chamber selectively communicates with either a breathing bag which can be squeezed by an attending anesthetist for manually as sisted ventilation or a mechanical ventilator for mechanically controlled ventilation. The pop-off valve control pressure is derived from the second chamber regardless of whether ventilation is manually assisted or mechanically controlled. By always deriving the popolf valve control pressure from the reservoir assembly second chamber rather than directly from the circuit, the following advantages are achieved:

1. The possibility of a high pressure in the circuit sealing the pop-off valve and creating an unsafe pressure condition is avoided;

2. The possiblity of crosscontamination is further reduced; and

3. The pop-off valve control mechanism can be more simply and inexpensively constructed since it need only respond to two, rather than three, control pressures.

In accordance with the preferred embodiment of the invention, the reservoir assembly is comprised ofa rigid container in which an inexpensive and disposable plastic or latex bag is mounted in communication with the circuit. The interior of the container outside of the plastic bag is pressurized by either a mechanical venti lator or a conventional breathing bag which can be manually squeezed by the anesthetist.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a general anesthesia rebreathing system disclosed in the parent application;

FIG. 2 is an enlarged perspective view better illustrating the disposable portion of the system of FIG. 1',

FIG. 3 is a schematic flow diagram of an anesthesia circle system in accordance with the teachings of the parent application;

FIG. 4 is a schematic flow diagram of a single tube (Magill type) anesthesia circuit system in accordance with the teachings of the parent application;

FIG. 5 is a side view, partially broken away, illustrating in detail the interface region of the system of FIG. 2 between the disposable and permanent portions;

FIG. 6 is a plan view, partially broken away, illustrating the interface region of the system shown in FIG. 5;

FIGS. 7A and 7B are sectional views taken substantially along the plane 7-7 of FIG. 5 respectively illustrating the different positions of the controller valve for coupling system pressure and ventilator pressure to the pop-off valve control ports;

FIG. 8 is a sectional view taken substantially along the plane 88 of FIG. 5 illustrating a third position of the controller valve;

FIG. 9 is a sectional view taken substantially along the plane 9-9 of FIG. 5 illustrating the valve element in the controller valve for varying the pop-off valve exhaust orifice;

FIG. 10 is a developed view illustrating the relationship between the controller valve spool element and the pop-off valve exhaust orifice as disclosed in the parent application;

FIG. II is a sectional view of one type of reservoir assembly disclosed in the parent application for isolating a mechanical ventilator from a patients gas;

FIG. 12 is a sectional view taken substantially along the plane l212 of FIG. 11;

FIG. I3 is a side elevational view illustrating the manner in which the reservoir assembly of FIGS. 11 and I2 is structurally incorporated in the system and further illustrating the incorporation of a canister of CO absorber material between the reservoir assembly and inspiratory valve;

FIG. 14 is a schematic flow diagram of an anesthesia circle system similar to that shown in FIG. 3 but modified in accordance with the teachings of the present invention;

FIG. I5 is a schematic flow diagram of a single tube (Magill type) anethesia circuit system similar to that shown in FIG. 4 but modified in accordance with the teachings of the present invention;

FIG. 16 is a perspective disassembled view of a preferred reservoir assembly embodiment in accordance with the present invention; and

FIG. 17 is a side sectional view of the preferred reser voir assembly embodiment of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing the apparatus illustrated in the figures, it is pointed out that FIGS. Il0 hereof are identical to the corresponding figures of the parent application. Further, FIGS. Ill3 hereof are identical to FIGS. I820 of the parent application. FIGS. 14-17 hereof illustrate the improvements in accordance with the present invention.

Attention is now called to FIG. 1 which illustrates a general anesthesia rebreathing system as disclosed in the parent application. Briefly. the rebreathing system as shown in FIG. I includes a substantially conventional anesthesia machine 10 which enables the attending anesthetist to meter and mix appropriate anesthetic agents which are then delivered to a supply hose 12 at an appropriate pressure, up to 50 psig. The gases supplied through hose 12 are then delivered through what is generally referred to as an anesthesia circuit 14 to the patient. The anesthesia circuit 14 functions to:

1. Carry the gases to the patient and communicate with the patient's airway via a mask or endotrachael tube;

2. Serve as a reservoir between the varying flow in and out of the patient and the constant rate of supply;

3. Eliminate excess gas from the system;

4. Reduce the inspired concentration of CO to ac ceptable levels; and

5. Enable the patients breathing to be assisted or controlled by manual or mechanical means.

The machine 10 is normally provided with sleeves I5 for holding a mounting arm I6 which functions as a support for the anesthesia circuit and pressure gauge 18.

As is well known, it is extremely difficult and imprac tical to fully sterilize all patient exposed parts of an anesthesia system after each usev As a consequence, it has long been recognized that utilization of anesthesia equipment presents a potential hazard of cross contamination between patients. In recognition of this potential hazard, efforts have been made in the prior art to fabricate the patient exposed parts sufficiently inexpensively to make disposal after a single use economically feasible. These attempts thus far have been only moderately successful because the required cost reductions have compromised performance and reliability. The parent application discloses an anesthesia system de signed to minimize the complexity and cost of the disposable portion while retaining within the disposable portion all of the elements which are likely to contaminate patient inspired gas. Briefly, two embodiments of disposable anesthesia circuits are disclosed which can interchangeably be easily coupled to a common perma nent system portion. The two anesthesia circuit embodiments represent modifications of circuits com monly known as (1) an anesthesia circle and (2) a sin gle tube anesthesia circuit (Magill type). In accordance with the present invention, the permanent system portion is comprised of the machine 10 including up to the free end of the mounting arm 16. The disposable portion of the system mates easily via a quick disconnect coupling to the free end of the mounting arm 16.

More particularly, with continuing reference to FIGv 2, the circuit 14 is coupled to the mounting arm 16 by a mounting unit 20 which will be described in greater detail hereinafter. The mounting arm 16 has an overflow (commonly referred to as a pop offfi valve 22 mounted near the free end thereof. As will be seen hereinafter, the operational mode of the valve 22 is selectable by the anesthetist by operation of a manual controller valve 24.

The mounting arm I6 and the elements fixed thereto. eg the pop-off valve 22 constitute part of the permanent or reusable portion ofa system in accordance with the preferred embodiment of the invention. The circuit 14 constitutes the disposable portion and includes all of the hardware elements between the mounting unit and the patient airway communication means, e.g. face mask 26. Briefly, the mounting unit 20 quickly connects and disconnects to the mounting arm 16 and provides gas flow paths therethrough to carry the gas supplied by hose 12 through the circuit 14 to the mask 26 and to carry CO rich gases expired by the patient to the pop-off valve 22. The circuit illustrated in FIG. 2 constitutes an anesthesia circle and the flow path therethrough will be discussed in connection with FIG. 3. To facilitate identification of elements, it is pointed out that the circuit 14 of FIG. 2 includes an inspiratory valve 28 which passes fresh gas supplied from the hose 12 by the arm 16, through an inspiratory tube 30, to a Y-piece 32 coupled to the mask 26. Also in communication with the inlet side of the inspiratory valve 28 is a gas reservoir or breathing bag 34.

The Y-piece 32 is also coupled to the inlet end of an expiratory tube 36 which has an expiratory valve in series therewith (not shown in FIG. 2). The oulct end of the expiratory tube 36 is coupled to the mounting unit 20 and communicates with the inlet side of the reservoir 34. The circuit further includes an overflow tube 38 extending from the Y-piece 32 back to the mounting unit 20 where it is in turn coupled to the input port of the pop-off valve 22.

Attention is now called to FIGS. 3 and 4 which respectively constitute schematic flow diagrams of two circuit embodiments in accordance with the invention disclosed in the parent application; namely, (1) an anesthesia circle (FIG. 3) and (2) a single tube Magill type circuit (FIG. 4). Prior to considering the gas flow paths through these two circuits, it is important to recognize that the gas exhaled by a patient can appropriately be considered to consist of dead space gas and alveolar gas. The dead space gas enters only the mouth, nose. and large passages in the lungs and does not interact with the blood flowing through the lungs. Therefore, dead space gas leaves the patient as it enters except for changes in temperature and humidity. It gives up no oxygen (0 or anesthetic agent and takes up no carbon dioxide (CO- On the other hand, alveolar gas does interact with the blood of the lung and it leaves the patient depleted in 0 and rich in CO In an adult having a tidal volume of 500 cc, 150 cc is normally dead space gas and 350 cc is normally alveolar gas. The circuits for FIGS. 3 and 4 are configured so as to retain the dead space and unbreathed gases within the system and preferentially vent the CO rich alveolar gases through the pop-0H valve 22. Thus, with a fresh gas inflow above 4 liters per minute, the inspired CO concentration remains acceptably low without requiring the use of CO, absorber material within the system.

Attention is now specifically called to FIG. 3 which depicts the flow paths through the anesthesia circle circuit embodiment. Dashed line 40 in FIG. 3 represents the interface between the disposable portion to the left and the permanent portion to the right. Fresh gas is supplied through tube 42 shown in FIG. 3 to the inlet side 43 of inspiratory valve 28. The fresh gas enters via a small orifice (not shown) with a high pressure drop across it, thus preventing any flow to and contamination of the permanent portion by the patients expired gas. The inlet side of inspiratory valve 28 also communicates with the reservoir 34. The inspiratory valve permits gas flow therethrough only in the direction indicated by the arrow shown at the outlet side thereof, thus allowing gas to be inspired by a patient from the inspiratory tube 30. Gas expired by the patient is applied to the inlet side of expiratory valve 44. The outlet side of expiratory valve 44 communicates with the previous mentioned overflow tube 38 and expiratory tube 36. The other end of expiratory tube 36 communicates at the anesthesia machine end of the system with the reservoir 34. The machine end of the overflow tube 38 communicates with the pop-off valve 22 constituting part of the system permanent portion.

In the operation of the anesthesia circle of FIG. 3, fresh gas flows into the circle via tube 42 and the inspiratory and expiratory valves 28 and 44 keep the flow around the circle unidirectional. When the patient breathes in or the reservoir 34 is squeezed, the inspiratory valve 28 opens, the expiratory valve 44 closes, and fresh gas and gas from the reservoir 34 and inspiratory breathing tube 30 flow into the patients airway via mask 26. When the patient breathes out, either spontaneously or because the pressure on the reservoir has been relaxed, the expiratory valve 44 opens and the inspiratory valve 28 closes and gas flows from the patient to the expiratory breathing tube 36 into the reservoir 34. At the same time, fresh gas enters via the fresh gas inlet 42 and flows primarily into the reservoir.

At some point during expiration during spontaneous ventilation, the reservoir 34 becomes full and the gas near the patient end of the circuit starts flowing through the overflow tube 38 and out the pop-off valve 22 which, during spontaneous ventilation, merely functions as a variable orifice pressure relief valve with an opening pressure of 1 cm. of H 0. This gas which is the last to leave the patient is alveolar gas which is rich in C0 The dead space gas, exhaled by the patient prior to expiration of the alveolar gas, is either further up the expiratory tube or in the distensible reservoir when the alveolar gas is exhaled.

Operation during manually assisted ventilation, i.e. when squeezing the reservoir, is similar to operation during spontaneous ventilation. However, flow out of the overflow tube 38 occurs during inspiration, i.e. when the reservoir is being squeezed, due to the pressure in the system. An alternative and preferred method of operation during manually assisted and controlled ventilation is to automatically positively close the pop-off valve 22 during inspiration when the reservoir is squeezed and permit it to open during expiration. As will be seen hereinafter when the operation of the pop-off valve is explained in connection with FIG. 5, an operational mode for the pop-off valve can he selected by the anesthetist such that when system pressure increases in response to the reservoir being squeezed, the pop-off valve 22 is sealed closed. Relaxation of the pressure on the reservoir 34 reduces the pressure within the circuit so that on expiration by the patient, the dead space gas will initially flow through the expiratory tube and into the reservoir 34 with the subsequently expired alveolar gas then flowing through the overflow tube 38 out the pop-off valve 22.

Thus, in summary, during spontaneous ventilation, the pop-off valve preferably comprises merely a variable orifice pressure relief valve which opens in response to pressure within the system. During manually assisted or controlled ventilation, the pop-off valve preferably seals closed in response to pressure within the system, ie inspiration.

As will be seen hereinafter, the operational mode of the pop-off valve 22 is determined by the pressure applied to a control port 47 thereof. This control pressure is selected by the anesthetist by manual control of a three way controller valve 24. The valve 24 enables any one of three control pressures to be available at an output port 49 for application to the pop-off valve control port 47 for determining the pop-off valve operational mode. Briefly, the control input port 47 of the pop-off valve 22 can be exposed to ambient pressure via valve 24 and tube 50. In this position of the three way valve, the pop-off valve 22 will function merely as a variable orifice pressure relief valve. During manually assisted or controlled ventilation, in order that the pop-off valve seals closed during inspiration, the valve 48 is positioned so as to couple tube 52 to the pop-off valve control port 47 to apply system pressure thereto. When using a mechanical ventilator, and the preferred reservoir embodiment, to be discussed hereinafter in connection with FIGS. Ill3, the pressure provided by the ventilator can be coupled through tube 54 and valve 24 to the pop off valve control port 47 to again assure that the pop-off valve 22 is closed when the system is being pressurized during inspiration.

Attention is now called to FIG. 4 which represents a schematic flow diagram ofa single tube anesthesia circuit often referred to as a Magill type circuit. A Magill type circuit is characterized by the utilization of a single breathing tube 60 in lieu of the inspiratory and expiratory breathing tubes 30 and 36 of a circle system as shown in FIG. 3. Thus, gas flow through the breathing tube 60 of FIG. 4 is alternately toward the patient on inspiration and away from the patient on expiration. The Magill type circuit of FIG. 4 does not require the utilization of the unidirectional inspiratory and expiratory valves as is characteristic of the circle system of FIG. 3.

During spontaneous ventilation, using the system of FIG. 4, as the patient breathes in, he draws fresh gas from the inlet tube 60 and the reservoir 64. On expira tion, his initially expired gas, constituting the dead space gas, will flow back through the breathing tube 60 to the reservoir 64. As the reservoir 64 becomes full, the subsequently expired alveolar gases will flow via the overflow tube 66 to the permanent pop-off valve 22. As has been previously pointed out, the permanent system portion can be used interchangeably with both the circle and single tube circuits of FIGS. 3 and 4.

During spontaneous ventilation utilizing the circuit of FIG. 4, the previously discussed pop-off valve 22 is operated in a variable orifice pressure relief mode by applying ambient pressure from tube 50 via three way valve 24 to the control port 47 of the pop-off valve. When ventilation is assisted or controlled by squeezing the reservoir 64, it is necessary to operate the popoff valve 22 so that it seals closed in response to a pressure increase during inspiration or otherwise CO rich gas will be retained within the system and fresh gas will exit through the pop-off valve. This operational mode is se lected by applying either system pressure from tube 52, via valve 24, to the pop-off valve control port 47 or by applying ventilator pressure via tube 54 and valve 24 to the control port 47.

Attention is now called to FIGS. 5 and 6 which illustrate the structural details of the free end of the mount' ing arm 16 and the mounting unit circuit portion 20 which couples to the arm I6.

The mounting arm 16 is provided with a nipple extending from the underside for coupling to the previously mentioned fresh gas supply hose 12. The nipple 70 communicates with a fresh gas passageway 72 extending parallel to the elongation of the arm I6. The passageway 72 opens at a front face 74 of the arm 16. An angular recess 76 is formed in the passageway 72 near face 74 and retains an O-ring 78 therein for sealing around a male tube member of the mounting unit 20 adapted to project into the passageway 72.

In addition to the passageway 72, the mounting arm 16 includes a passageway 80 which also opens at the front face 74 of the arm 16. An annular recess 82 is formed in passageway 80 near face 74 and it too retains an O-ring 84 for sealing around a male tube member of mounting unit 20, to be discussed hereinafter.

As was indicated with reference to FIGS. 4 and 5, the three way controller valve 24 functions to control the operational mode of the pop-off valve 22. The control ler valve 24 is manually operable to selectively communicate any one of the three previoulsy mentioned control sources to a control port of pop-off valve 22. In a first position, ambient pressure is applied to the control port, in a second position circuit pressure is applied to the control port and in a third position, ventilator pres sure is applied to the control port. As will be seen, means are provided for automatically assuring that the pop-off valve output orifice is fully open when either circuit or ventilator pressure is applied to the control port, corresponding to the operational modes used during manually assisted and controlled ventilation. On the other hand, when applying ambient pressure to the control port primarily used during spontaneous ventilation, means for varying the size of the pop-off valve output orifice are automatically moved into appropriate position.

With continuing reference to FIGS. 5 and 6, the popoff valve 22 includes an input port 92 extending through externally threaded nipple 93, an output port 94, and the previously mentioned control port 47. The nipple 93 is threaded into the arm I6 and communicates the input port 92 with the circuit pressure in passageway 80. The output port 94 is coupled by a short tube 95 to an exhaust input port 96 in the housing of controller valve 24. The control port 47 is coupled by a short tube 97 to previously mentioned port 49 of the controller valve 24.

The pop-off valve 22 includes a housing comprised of upper portion 98 threaded into lower portion 99 which in turn is threaded into nipple 93. A flexible diaphragm 100 is held around its circumference between opposed surfaces of housing portions 98 and 99. Disc 101, bearing against the underside of the diaphragm, has a rod I02 depending therefrom. The rod 102 extends through, in sealed relationship, a fixed wall 103 and into a recess defined in boss 104 formed in valve leaf I05. A coil spring I06 is contained around rod 102 between wall 103 and disc 101.

In the operation of the pop-off valve 22, when ambient pressure is available on the upper surface of diaphragm 100, the spring 106, will force the rod I02 to the position shown in FlG. 5, in which its end is spaced from the bottom of the recess in boss 104 of valve leaf 105. As a consequence, valve leaf 105 which normally rests on and seals against knife edge 107 on nipple 93 will be lifted when the pressure within passageway 80 exceeds a first threshold, e.g., 1 cm. of H 0, to permit gas flow from passageway 80 out through port 94.

On the other hand, when a positive pressure is applied to the upper surface of diaphragm 100 (from the circuit or ventilator via the controller valve 24, as will be discussed hereinafter), the diaphragm 100 will be bowed downwardly to bottom rod 102 in the recess in boss 104 thereby positively sealing valve leaf 105 against knife edge 107. It is pointed out that the active area of diaphragm 100 is greater than the active area of valve leaf 105 and as a consequence, the valve leaf 105 will be sealed closed when equal pressures are applied through the control port 47 and input port 92 and the pressure on the diaphragm exceeds a second threshold, e.g., S cm. of H 0.

The controller valve 24 functions to enable an anesthetist to selectively apply either ambient pressure, circuit presssure or ventilator pressure to the control port 47 for operating the pop-off valve in the aforedescribed manner. As will be seen, when ambient pressure is applied, the controller valve 24 also enables the anesthetist to vary the size and thus the flow rate out of the pop-off valve output port 94. When circuit pressure or ventilator pressure is applied, the output port 94 is left fully open.

The controller valve 24 comprises a spool valve having a housing comprised of an upper portion 107' threaded onto a lower portion 108. Lower portion 108 has an externally threaded nipple 109 threaded into arm 16. Nipple 109 has a central bore therethrough which communicates the exhaust input port 96 through arm 16 to nipple 110. A system exhaust hose 111 is intended to be coupled into nipple 110 for carrying ex hausted gas away, preferably out of the operating room, to prevent any adverse effect upon the personnel present.

From what has previously been said, it should be recognized that three different pressure sources (including ambient) are applied to the input side of controller valve 24 for selective coupling by the anesthetist to the port 49 for communication through tube 97 to the popoff valve control port 47. One of these three sources comprises circuit pressure (corresponding to tube 52 in FIG. 3) which is available through nipple 112 via a hose 113 from nipple 114 in communication with passageway 80 through arm 16. A second of the sources is derived from ventilator pressure (corresponding to tube 54 in FIG. 3) through nipple 115 and will be discussed in greater detail in connection with the description of FIGS. 1113.

Communication from either nipple 1 12 or nipple 115 to port 49 is controlled by the position of a spool 116 mounted for rotation within lower housing portion 108. Spool 116 has a shaft 117 coupled thereto which in turn is connected to a knob 118 available for manual rotation by the anesthetist. The inner surface of housing portion 106 is provided with annular recesses 118 and 119 each of which retains an O-ring 120. Spool 116 is provided with a slot 12] extending around a portion of the circumference thereof of sufficient length to bridge the distance between nipples 112 and 115 and port 49. More particularly, with the spool rotated to the position of FIG. 7A. slot 121 will communicate nipple with port 49. When spool 116 is rotated to the po sition of FIG. 78, slot 121 communicates ripple 112 with port 49. In order to facilitate the ancsthetists positioning of the spool, the knob 118 is preferably pro vided with a pointer 122 which can be appropriately detented in two positions.

In order to selectively communicate a third pressure source, i.e., ambient (correpsonding to tube 50 of FIG. 3) with port 49 the spool 116 is provided with an additional slot 123 extending greater than 180 around the circumference thereof. The slot 123 is vertically displaced from the slot 121 but is still able to communicate with port 49 (see FIG. 8) as a consequence of the provision of vertical slot 124 in communication with port 49. Slot 123 communicates with ambient pressure via passageway 126 through the spool 116, shaft 117 and knob 118. Inasmuch as it is necessary to prevent communication between slots 121 and 123, the spool circumferential surface and the lower housing portion inner surface are correspondingly tapered and a spring 127 is provided around shaft 117 to seat the spool in the tapered housing so that the housing inner surface seals the slots.

As previously pointed out, it is desirable to enable the anesthetist to variably control the flow out of the pop off valve exhaust port 94 when the pop-off valve is being operated in the pressure relief mode to assure the maintenance of an adequate gas supply within the circuit. On the other hand, when the pop-off valve is being operated in the balanced mode it is desirable that the pop-off valve exhaust be wide open. In order to accomplish this, the spool is provided with a valve member 128 depending from the lower end thereof and shaped so as to variably cover the port 96 as the knob 118 and spool 116 are rotated. The variable covering of the ort 96 can best be seen in the developed view of FIG. 10 which shows how the valve member 128 wipes across the port 96. Note that the valve covers the port 96 only when slot 123 communicates with port 49 and is re' mote from and has no effect on the port 96 when the slot 121 is in communication with port 49.

The front face 74 arm of the mounting arm 16 is provided with a pair of forwardly projecting pins 130 each of which has an annular groove 131 formed therein at the forward end thereof. These pins 130 are utilized to align and retain the mounting unit 20 relative to the arm 16 so as to provide mechanical support and gas flow communication therebetween.

Attention is now called to FIGS. 11 and 12 which illustrate a preferred reservoir embodiment in accor dance with the present invention. As has been previ ously mentioned herein, the reservoir thus far referred to, can constitute a conventional single compartment breathing bag. However, although such a bag might be adequate for spontaneous and manually assisted venti lation, it would not be satisfactory for controlled ventilation where the reservoir is squeezed by a mechanical ventilator since the ventilator would then be exposed to the patients gas and would constitute an avenue for cross-contamination between patients.

Accordingly, a reservoir 300 is provided, as illustrated in FIGS. 1 1-13, which isolates the ventilator from the patients gas. The reservoir 300 includes a pair of hermetically isolated chambers which respectively communicate with the anesthesia circuit and the ventilator. The reservoir 300 preferably is formed utlizing three layers of vinyl sheeting 302, 304 and 306 which are welded to each other and to fittings 308 and 310. The fitting 310 communicates with a chamber 312 formed between sheets 302 and 304 and the fitting 308 communicates with a chamber 314 formed between the sheets 304 and 306. The fitting 308 is a 22 millimeter fitting adapted to force fit onto tapered male nipple 132 of the the mounting unit 20 as represented in FIGS. 5 and 7. The fitting 310 is provided with a terminal taper 311 intended to be force fit into the end of a corrugated tube 320 which in turn is coupled to a mechanical ventilator (not shown).

In the use of the ventilator isolator reservoir 300 of FIGS. 11-13, the ventilator will periodically pressurize the chamber 312. The pressure on the isolating septum sheet 304 will be transmitted to the chamber 314 thereby producing a corollary pressure within the inspiratory breathing tube 30. The outer sheets 302, 304, 306 of the reservoir 300 of FIGS. 11 and 12 should be thin, flexible and inelastic. The exterior contour of the reservoir 300 is preferably similar to the contour of conventional breathing bags so that the feel is similar. The septum sheet 304 is preferably contoured similar to sheets 302 and 306 so that it may sweep the en tire volume of reservoir 300 with minimal pressure dif ferential across the septum sheet. Preferably, the se ptum sheet 304 should be a visible color and at least one outer sheet should be transparent so that volume changes caused by movement of the septum sheet can be readily observed by the attending anesthetist. By providing the reservoir 300 with thin and flexible outer walls, it will function as a conventional breathing bag during manually assisted ventilation since it can be readily squeezed by the anesthetist and the conventional feel will only be minimally modified by the presence of the septum sheet 304.

It has previously been mentioned with respect to the operation of the pop-off valve 22 that it is preferable, under conditions of controlled ventilation, to make the pop-off valve responsive to ventilator pressure. That is. it will be recalled that when the system is pressurized by the ventilator during inspiration. it is desirable to close the pop-off valve. It will further be recalled that for this purpose, reference was made to a tube 54 in FIG. 2 coupled to the input side of the three way controller valve 24, i.e. to nipple 115 in FIG. 6. In order to communicate the ventilator pressure to the nipple 115, a nipple 322, in communication with chamber 312, is provided within sheet 302 of reservoir 300. One end of the tube 54 fits onto the nipple 322. Alternately, pressure may be supplied to tube 54 from a side port nipple on the tapered 22 millimeter male fitting 311 which connects corrugated tube 320 to the ventilator chamber 312 of the reservoir 300.

It has been previously pointed out that utilization of the overflow tube in the manner indicated to preferentially vent alveolar gases eliminates the need to use CO absorber material under most circumstances. However. it has also been recognized that special circumstances (cg. fresh gas inflow less than 4 liters per minute) or personal preferences of the anesthetist may dictate that CO absorber material be used. Thus. a canister 350 (FIG. 13) is provided for optional incorporation between the tapered male nipple 133 of the mounting unit and the tapered female opening in inspiratory valve 28.

As previously mentioned. the apparatus illustrated in FIGS. I-13 hereofis disclosed in applicants parent application. Attention is now called to FIGS. 14 and 15 which schematically illustrate the improved anesthesia rebrcathing systems in accordance with the present invention. It will be recognized that FIG. 14 illustrates an anesthesia circle system similar to that previously discussed in connection with FIG. 3 and FIG. 15 illustrates a single tube anesthesia circuit system similar to that previously discussed in connection with FIG. 4. Elements in FIGS. 14 and 15 corresponding to elements in FIGS. 3 and 4 are identified by the same designation numerals preceded by the digit Thus. for example. the overflow tube 38 of FIG. 3 is designated by the numerals 538 in FIG. 14. Elements in FIGS. 14 and 15 which do not have an identical counterpart in FIGS. 3 and 4 will be identified by a designating numeral begin ning with 4.

The embodiment of FIG. 14 requires utilization of a two chamber reservoir assembly 400, for example of the type illustrated in FIGS. 11-13, or preferably. of the type to be discussed hereinafter in connection with FIG. 16. The reservoir assembly 400 is comprised of an outer wall means 402 defining a certain volume and an inner wall means 404 disposed therein to partition the volume into first and second hermetically isolated chambers 406 and 408. The inner wall means 404 is flexible so as to enable pressure levels to be transferred therethrough as has been previously mentioned with respect to the structure of FIGS. 1113. The first chamher 406 communicates with the breathing tubes at the second end thereof. The second chamber 408 opens into a fitting 410 which can selectively communicate through tubing 411 and selector valve means 412 either with a squeezable container 414 or a mechanical ventilator 416.

Prior to considering the operation of the system as represented in FIG. 14, it is important to note that the embodiment of FIG. 14 differs from the embodiment of FIG. 3 by the absence of tube 52 which. it will he recalled, couples breathing circuit pressure to one input port of the controller 24 in FIG. 3.

It will further be recalled that in the system of FIG. 3, the anesthetist can manually operate the controller 24 to select any of three sources to apply to the control port of pop-off valve 22. That is. for spontaneous venti lation, ambient pressure is applied to the control port of pop-off valve 22 via tube 50. For manually assisted ventilation. system pressure available through tube 52 is applied to the pop-off valve control port. For mechanically controlled ventilation. mechanical ventilator pressure available through tube 54 is applied to the pop-off valve control port.

In accordance with the present invention. tube 52 of FIG. 3 is eliminated and the pop-off valve controller. for both manually assisted and mechanically controlled ventilation. applies the pressure from the second chamber 408 of the reservoir assembly 400 to the pop-off valve control port. Thus. the pop-off controller (524 in FIG. 14) need only comprise a two input port device rather than the three input port device represented in FIGS. 4-9. Thus. for simplicity. the controller 524 of FIG. 14 can be considered as being identical in construction to the controller 24 illustrated in FIGS. 5-9 except that the port 112 is sealed closed.

The operation of the system of FIG. 14 is identical to the operation of the system of FIG. 3 for spontaneous ventilation. For manually assisted ventilation, the attending anesthetist will operate the two position valve 412 to communicate the second chamber 408 of the reservoir assembly 400 with the interior of the container 414. The container 414 can comprise a conventional breathing bag which can be squeezed by the anesthetist. A source of working gas 418 is coupled through a valve 420 to the fitting 410 to enable the anesthetist to fill the volume of the second chamber 408, container 414 and communicating tubes therebetween. With these volumes filled, the anesthetist can now periodiclly squeeze the container 414. As the container 414 is squeezed, the pressure is increased in the second chamber 408. The increase in pressure is communicated through the wall 404 to the first chamber 406 to open the inspiratory valve 528 and pen'nit gas flow to the patient via breathing tube 530. In addition, the increased pressure in the second chamber 408 is communicated via tube 554 to the controller 524 to seal the pop-off valve 522. When the anesthetist relaxes the pressure on the container 414, the inspiratory valve 528 closes, the expiratory valve 544 opens, and the pressure is also relieved from the pop-off valve thereby enabling the patients expired alveolar gases to flow through overflow tube 538 and out of the pop-off valve 522.

In the mechanically controlled mode of ventilation, the anesthetist will switch the position of the manually controlled two position valve 412 to couple the mechanical ventilator 416 to the reservoir assembly second chamber 408. The mechanical ventilator 416 will then periodically increase the pressure in chamber 408 in a manner directly analogous to that produced by the anesthetist in squeezing the container 414 during the manually assisted mode.

Thus, it should be appreciated that although the system of FIG. 14 operates similarly to the system of FIG. 3 in the spontaneous and mechanically controlled ventilation modes, it represents a significant improvement thereover in that it avoids the necessity of employing tube 52 of FIG. 3 to couple system pressure to the popoff valve controller. Elimination of tube 52 of FIG. 3 yields several advantages:

1. It avoids the possibility of a high pressure in the breathing tubes sealing the pop-off valve so as to create a physiologically unsafe condition;

2. It avoids exposing the controller to the patients gases and thereby eliminates a remote possibility of cross-contamination; and

3. It enables the utilization of structurally simpler two input port controller as contrasted with the three input port controller required in the embodiment of FIG. 3.

Attention is now called to FIG. 15 which illustrates a single tube rebreathing system of the type represented in FIG. 4 which has been modified in the same manner as was the system of HG. 3. That is, it will be noted that the system of HQ 15 differs from the system of FIG. 4 by elimination of tube 52 of FIG. 4. The operation of the system of HG. 15 is identical to that described in connection with FIG. 4 except that during the manually assisted ventilation mode, the attending anesthetist will squeeze container 414 rather than container 64 as represented in FlG. 4.

Attention is now called to FIGS. 16 and 17 which illustrate a preferred embodiment of the reservoir assembly 400 schematically illustrated in FIGS. 14 and 15. From the operational description of the system of FIGS. 14 and 15, it should be recognized that during manually assisted ventilation, the attending anesthetist squeezes container 414 to periodically increase the pressure within the second chamber 408 of the reservoir 400. These periodic pressure increases are communicated from chamber 408 to chamber 406 through the wall 404. It is important to note that the anesthetist need not squeeze the reservoir 400.

In recognition of the foregoing, a preferred reservoir assembly, as represented in FIGS. 16 and 17, is provided comprised of a rigid container 430. The container is preferably cylindrical and defines top and bottom walls 432 and 434 and a circumferential wall 436. The walls 432, 434 and 436 envelop a fixed volume 438. Top wall 432 defines an opening 440 surrounded by an upstanding flange 442 preferably supporting O- ring 443. Openings 444 and 446 are formed in wall 436, in communication with fittings 448 and 450, for coupling to the tubes 554 and 411 illustrated in FIG. 14.

The portion of the reservoir assembly of FIGS. 16 and 17 thus far described constitutes part of the permanent system hardware since it is not exposed to the patients gas. The disposable portion 460 of the reservoir assembly for use with the container 430 includes a lid 462 configured so as to fit over the flange 442 to seal the opening 440. A tubular fitting 464 is formed in the lid 462 and at its lower end opens into a bag 466. The upper end of fitting 464 is intended to be coupled to the second end of the breathing tube 536 (FIG. 14) proximate to the inspiratory valve 528.

It should be recognized from the structural configuration described that the bag 466 defines the first chamber discussed in FIG. 14 and the volume within the container 430 outside of the bag 466 defines the second chamber. In the use of the reservoir assembly, only the disposable portion 460 is exposed to the patients gas. Accordingly, by disposing of the portion 460 after each use, the possibility of crosscontamination via the reservoir assembly is eliminated. It should further be recognized that the disposable portion 460 can be very inexpensively formed of plastic material, for example.

From the foregoing, it should be appreciated that an improved general anesthesia rebreathing system has been disclosed herein comprised of a disposable portion and a permanent portion and configured so as to minimize the cost and complexity of the disposable portion, while including within the disposable portion all of the elements likely to produce crosscontamination.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An anesthesia system for coupling a fresh gas supply means to a patients airway, said system including:

elongated breathing tube means having an open first end adapted to communicate with said airway and an open second end adapted to communicate with said supply means, said breathing tube means providing a flow path in the direction from said airway to said supply means and from said supply means to said airway;

overflow valve means having an input port and an exhaust port and including valve element means normally seated to hermetically isolate said input and exhaust ports and responsive to a positive pressure exceeding a first threshold from said input to said exhaust side of said valve element means for unseating said valve element means to pemiit gas flow therepast;

means mounting said overflow valve means in close proximity to said elongated breathing tube means second end;

elongated overflow tube means, substantially coextensive with said breathing tube means, having an open first end in communication with said breathing tube means in close proximity to the first end thereof and an open second end coupled to said overflow valve means input port, said overflow tube means providing a flow path in the direction from said breathing tube means to said overflow valve means;

a reservoir assembly including outer wall means enclosing a volume and inner wall means partitioning said volume into first and second hermetically isolated chambers, said inner wall means being flexible for transmitting pressures between said chambers;

means for communicating said first chamber with said breathing tube means second end;

said overflow valve means including a control port and means responsive to the application of a positive pressure exceeding a second threshold to said control port for seating said valve element means independent of the pressure differential between said input and exhaust sides of said valve element means;

means for selectively communicating the pressure in said second chamber to said control port;

container means having a flexible wall capable of being manually squeezed to increase the pressure therein; and

means for communicating the pressure in said container means to said reservoir assembly second chamber.

2. The system of claim 1 wherein said means for communicating the pressure in said container means to said second chamber includes a manual valve means having first and second input ports and on an output port;

means coupling said output port to said second chamber;

means coupling said container means to said first input port; and

means adapted to couple said second input port to a mechanical ventilator.

3. The system of claim 1 wherein said reservoir assembly outer wall means is rigid.

4. The system of claim 1 including an opening in said reservoir assembly outer wall; and

lid means adapted to fit over and seal said opening, said lid means including a fitting extending into said volume and a flexible bag detachably sealed to said fitting.

5. The system claim 1 wherein said means for selec tively communicating said second chamber to said con trol port includes a controller means having selectable first and second input ports and an output port;

means coupling said controller means output port to said control port;

means coupling said second chamber to said control ler means first input port; and

means exposing said controller means second input port to ambient pressure.

6. The system of claim 1 wherein said breathing tube means includes first and second breathing tubes having open first and second ends;

patient communication means defining a passageway therethrough having first and second open ends;

means forming a gas flow path between the first ends of said first and second breathing tube means and the first end of said passageway; and

means for communicating the second end of said second breathing tube means with said reservoir assembly first chamber.

7. Anesthesia rebreathing apparatus useful in combination with a source of fresh anesthesia gases, said apparatus comprising:

a gas overflow valve, having input and exhaust ports,

mounted proximate to said fresh gas source;

elongated breathing tube means having an open second end adapted to communicate with said fresh gas source and an open first end adapted to communicate with a patients airway, said breathing tube means providing a flow path in the direction from said airway to said fresh gas source and from said gas source to said airway;

an elongated overflow tube means of substantially the same length as said breathing tube means, hav ing an open first end in communication with said breathing tube means proximate to the first end thereof and an open second end in communication with said overflow valve input port, said overflow tube means providing a flow path in the direction from said breathing tube means to said overflow valve;

a reservoir assembly including outer wall means enclosing a volume and inner wall means partitioning said volume into first and second hermetically isolated chambers, said inner wall means being flexible for transmitting pressures between said chambers;

container means having a flexible wall capable of being manually squeezed to increase the pressure therein;

means for communicating the pressure in said container means to said reservoir assembly second chamber; and

means for communicating said first chamber with said breathing tube means second end.

8. The apparatus of claim 7 wherein said reservoir assembly outer wall means is rigid.

9. The apparatus of claim 7 wherein said means for communicating said first chamber with said breathing tube means second end includes a fitting extending into said volume through said reservoir assembly outer wall means; and wherein said inner wall means comprises a flexible bag detachably sealed to said fitting.

10. The apparatus of claim 7 wherein said breathing tube means includes first and second breathing tubes having open first and second ends;

patient communication means defining a passageway therethrough having first and second open ends;

means forming a gas flow path between the first ends of said first and second breathing tube means and the first end of said passageway; and

means for communicating the second end of said second breathing tube means with said reservoir assembly first chamber. 

1. An anesthesia system for coupling a fresh gas supply means to a patient''s airway, said system including: elongated breathing tube means having an open first end adapted to communicate with said airway and an open second end adapted to communicate with said supply means, said breathing tube means providing a flow path in the direction from said airway to said supply means and from said supply means to said airway; overflow valve means having an input port and an exhaust port and including valve element means normally seated to hermetically isolate said input and exhaust ports and responsive to a positive pressure exceeding a first threshold from said input to said exhaust side of said valve element means for unseating said valve element means to permit gas flow therepast; means mounting said overflow valve means in close proximity to said elongated breathing tube means second end; elongated overflow tube means, substantially coextensive with said breathing tube means, having an open first end in communication with said breathing tube means in close proximity to the first end thereof and an open second end coupled to said overflow valve means input port, said overflow tube means providing a flow path in the direction from said breathing tube means to said overflow valve means; a reservoir assembly including outer wall means enclosing a volume and inner wall means partitioning said volume into first and second hermetically isolated chambers, said inner wall means being flexible for transmitting pressures between said chambers; means for communicating said first chamber with said breathing tube means second end; said overflow valve means including a control port and means responsive to the application of a positive pressure exceeding a second threshold to said coNtrol port for seating said valve element means independent of the pressure differential between said input and exhaust sides of said valve element means; means for selectively communicating the pressure in said second chamber to said control port; container means having a flexible wall capable of being manually squeezed to increase the pressure therein; and means for communicating the pressure in said container means to said reservoir assembly second chamber.
 2. The system of claim 1 wherein said means for communicating the pressure in said container means to said second chamber includes a manual valve means having first and second input ports and on an output port; means coupling said output port to said second chamber; means coupling said container means to said first input port; and means adapted to couple said second input port to a mechanical ventilator.
 3. The system of claim 1 wherein said reservoir assembly outer wall means is rigid.
 4. The system of claim 1 including an opening in said reservoir assembly outer wall; and lid means adapted to fit over and seal said opening, said lid means including a fitting extending into said volume and a flexible bag detachably sealed to said fitting.
 5. The system claim 1 wherein said means for selectively communicating said second chamber to said control port includes a controller means having selectable first and second input ports and an output port; means coupling said controller means output port to said control port; means coupling said second chamber to said controller means first input port; and means exposing said controller means second input port to ambient pressure.
 6. The system of claim 1 wherein said breathing tube means includes first and second breathing tubes having open first and second ends; patient communication means defining a passageway therethrough having first and second open ends; means forming a gas flow path between the first ends of said first and second breathing tube means and the first end of said passageway; and means for communicating the second end of said second breathing tube means with said reservoir assembly first chamber.
 7. Anesthesia rebreathing apparatus useful in combination with a source of fresh anesthesia gases, said apparatus comprising: a gas overflow valve, having input and exhaust ports, mounted proximate to said fresh gas source; elongated breathing tube means having an open second end adapted to communicate with said fresh gas source and an open first end adapted to communicate with a patient''s airway, said breathing tube means providing a flow path in the direction from said airway to said fresh gas source and from said gas source to said airway; an elongated overflow tube means of substantially the same length as said breathing tube means, having an open first end in communication with said breathing tube means proximate to the first end thereof and an open second end in communication with said overflow valve input port, said overflow tube means providing a flow path in the direction from said breathing tube means to said overflow valve; a reservoir assembly including outer wall means enclosing a volume and inner wall means partitioning said volume into first and second hermetically isolated chambers, said inner wall means being flexible for transmitting pressures between said chambers; container means having a flexible wall capable of being manually squeezed to increase the pressure therein; means for communicating the pressure in said container means to said reservoir assembly second chamber; and means for communicating said first chamber with said breathing tube means second end.
 8. The apparatus of claim 7 wherein said reservoir assembly outer wall means is rigid.
 9. The apparatus of claim 7 wherein said means for communicating said first chamber with said breathing tube means second end includes a fitting extending into said volume through said reservoir assembly outer wall means; and wherein said inner wall means comprises a flexible bag detachably sealed to said fitting.
 10. The apparatus of claim 7 wherein said breathing tube means includes first and second breathing tubes having open first and second ends; patient communication means defining a passageway therethrough having first and second open ends; means forming a gas flow path between the first ends of said first and second breathing tube means and the first end of said passageway; and means for communicating the second end of said second breathing tube means with said reservoir assembly first chamber. 